1. Technical Field
The present invention relates generally to Pedestrian Dead Reckoning (PDR) and, more particularly, to a method and apparatus that receive step length estimation model parameters from a server and utilize the parameters when a terminal (user equipment: UE) including sensors, such as an accelerometer, a gyroscope, and a magnetometer, calculates its location through PDR for estimating a step count, a step length, and direction (heading) information using the sensors, thus promptly and accurately providing location information immediately upon receiving a location request, without requiring an additional calibration operation in the user equipment. Further, the present invention relates to a method by which the user equipment including sensors provides sensor measurement information per step to the server.
2. Description of the Related Art
In future mobile communication services, it will be very important to accurately and reliably determine the absolute or relative location of mobile communication user equipment (UE). In particular, in the case of precise positioning methods, such as the E-911 (Enhanced 9-1-1) service in the United States, there are increased needs for methods which serve commercial purposes, disaster management purposes, such as for emergency relief, or military application purposes.
Mobile carriers or UE manufacturers have conducted research into technology for providing precise positioning regardless of the environment of users of UE. In particular, Pedestrian Dead Reckoning (PDR) is a positioning method that may be usefully utilized in an environment in which a Global Positioning System (GPS) and a mobile communication infrastructure are not present, or in which location accuracy is deteriorated upon performing positioning based on the corresponding infrastructure.
PDR is a method of providing relative location information, but if an absolute location at a point in time when positioning is performed is known, absolute locations may be continuously provided based on the absolute location. Generally, PDR is configured to estimate distance, heading, etc. per walking step using measurement information obtained from the accelerometer, gyroscope, magnetometer (digital compass), etc. of UE used by a pedestrian. Typically, distance per walking step is obtained using a step length, and heading per walking step is obtained using either the orientation information of the magnetometer or information obtained by integrating angular velocity output of the gyroscope.
PDR is divided into a step estimation procedure for estimating a step count (the number of steps) and a step length, and a heading estimation procedure for estimating the heading.
The step estimation procedure is subdivided into a procedure for estimating a step count using a maximum value, a minimum value, a variance, etc. of the output value of the accelerometer per walking step and a procedure for estimating a step length indicating a movement distance between continuous steps. In particular, in the case of the procedure for estimating a step length, when a location error occurs, the location error is continuously accumulated as walking continues, and so the accuracy of the step length is very important in precise positioning. Generally, a step length is influenced by the motional state of a pedestrian (for example, slow walking, quick walking, slow running, quick running, climbing up, climbing down, ascending stairs, descending stairs, etc.) or motional characteristics such as height, gender, and walking features (for example, straight line walking or out-toed gait). Therefore, in order to exactly reflect the characteristics of a pedestrian, off-line calibration is required which calibrates an estimated step length while moving in a designated interval or between reference locations before positioning is started.
In an environment in which an absolute location can be provided by an outdoor Global Positioning System (GPS) or an indoor WiFi infrastructure, on-line calibration may also be performed by applying the corresponding location information to a step length estimation procedure.
In a heading estimation procedure, the heading of the UE is estimated using the output value of a magnetometer or a gyroscope. Since these two types of sensors have contrary measurement characteristics, they may be complementarily operated to improve the accuracy of heading information.
That is, the magnetometer has an advantage of providing absolute orientation, but reacts sensitively to a surrounding environment influencing the gyroscope, and thus a large error may occur. Meanwhile, since the gyroscope outputs angular velocity information, it reacts promptly to a sudden heading change of a pedestrian, but has a disadvantage of increasing an error in heading information as a step count increases, because relative orientation is estimated using integral calculus.
Generally, when off-line calibration is applied to a step length estimation procedure, there is inconvenience in that the user of normal UE must perform a separate calibration procedure so as to use location information. For such calibration, the location of a designated interval or reference locations must be accurately known, and then the convenience of service usage is deteriorated. Further, when on-line calibration is applied, there is a disadvantage in that it is difficult to receive GPS signals, and in that in an indoor environment in which a wireless communication infrastructure, such as a WiFi infrastructure, is not installed, such calibration cannot be performed.
Therefore, a new step length estimation technique capable of estimating more precise step length information without undergoing off-line or on-line calibration is urgently required.